Concept reference

Screening and Solids Handling

C.1Plain-language definition

Screening moves a solids problem; it does not make it disappear. Intercepted material must be lifted, washed or drained, stored and removed safely. Unscreened material must pass through pumps, valves and the force main without ragging or settling. The defensible strategy follows the material from arrival to final disposal.

C.2Governing relation or decision logic

A screen’s hydraulic check uses approach and through-screen velocity, open area and increasing loss as blinding reduces that area. A pump solids-passage check uses the minimum free passage through the actual impeller and casing geometry. Neither has one universal acceptable dimension; influent character, equipment testing and owner practice govern.

C.3The failure to name

Specifying a clear opening but ignoring blinding can produce upstream surcharge. Calling a pump “non-clog” without tracing its minimum passage or rag behaviour transfers maintenance into a submerged machine. Fine screens without handling equipment create a manual lifting hazard.

C.4Field review checklist

• Characterise rags, wipes, grit, large debris and peak wet-weather load.
• Trace captured or passed material through every downstream component.
• Check clean and blinded hydraulic conditions plus bypass/overflow consequence.
• Provide safe access, lifting, washdown, drainage, storage and disposal operations.

C.5Where it fits in the course

§8.2 compares intercept-versus-pass strategies; §6.3 examines pump passage.